S. Mustafa

Surface properties of the mixed oxides of iron and silica

Amorphous synthetic mixed oxides of iron and silicon of varying composition (1.5 M SiO2:0.5 M Fe(OH)3, 0.5 M SiO2:0.5 M Fe(OH)3, 0.5 M SiO2:1.5 M Fe(OH)3) were prepared by sequential precipitation and their surface properties were explored. The Fourior transform infrared (FTIR), X-ray differactometry (XRD), Electron scanning microscopy (SEM), Electron probe micro-analysis (EPM) and Surface area measurement were used to characterize the synthetic mixed oxides. The point of zero charge (PZC) was determined by the salt addition and fast titration techniques. In the present investigation, the focus was on the surface charge, surface dissociation constants and PZC determination from the potentiometric titration data in the temperature range 293–323 K. During this study two common intersection points (CIPs) and two PZCs were observed for the mixed oxides, one corresponding to SiO2 and other to Fe(OH)3.

Effect of phosphate complexation on Cd2+ sorption by manganese dioxide (β-MnO2)

Sorption of metal ions on oxide/hydroxide surfaces mediates the fate and transport of these ions in many natural systems. These metallic ions often exist in bulk in the aqueous phase as complexes with inorganic and organic ligands. In the present study, we investigated the sorption properties of manganese dioxide in the presence of phosphate which is thought to be one of the most important complex forming species. The surface area, point of zero charge and structural morphology of the solid manganese dioxide were determined. Cd(2+) sorption studies were carried out on manganese dioxide as a function of pH, temperature and phosphate concentration. Cd(2+) sorption increased with increasing pH, temperature and phosphate concentration. It was found that phosphate formed both outer and inner sphere complexes via metal and ligand-like adsorption. The Langmuir equation was applied to describe the data and from the constants of this equation different thermodynamic parameters such as DeltaH(0), DeltaS(0) and DeltaG(0) were evaluated.

Chromium (III) removal by weak acid exchanger Amberlite IRC-50 (Na)

Chromium (III) sorption on a weakly macroporous cation exchanger Amberlite IRC-50 (Na) is studied as a function of time and temperature. The rate constant values for chromium (III) sorption are calculated both for film and particle diffusion processes. The temperature is found to have a positive effect on both the diffusional processes. The high values of energy of activation confirm the particle diffusional nature of the process. The pH changes in the system show a competition between the Cr(OH)(2+) and H(+) ions for the exchange sites of the adsorbent. Equilibrium data are explained with the help of Langmuir equation. Various thermodynamic parameters (DeltaH degrees , DeltaS degrees and DeltaG degrees) from chromium (III) exchange on the resin are calculated.

Cation exchange removal of Pb from aqueous solution by sorption onto NiO

This paper reports NiO as a novel and an efficient adsorbent for the removal of Pb from aqueous solutions. In the present investigation, Pb adsorption experiments on NiO were conducted on aqueous solution at different initial Pb concentration, pH of the solution and adsorption temperature. The mechanism of adsorption was observed to be an ion exchange between the surface proton and Pb in aqueous solution. Experimental data were best described by the Langmuir isotherms. The surface structure of the NiO before and after adsorption of Pb was analyzed by using FTIR spectroscopy, scanning electron microscopy (SEM) coupled with energy dispersive X-ray analyses (EDX).

Removal of Co2+ ions from aqueous solution by cation exchange sorption onto NiO

Batch adsorption technique was used to study the adsorption of cobalt on NiO. The aim of this work was to examine the effect of pH, concentration and temperature on the ion exchange removal of Co2+ from aqueous solution by the NiO surface. We used Langmuir model to interpret the adsorption data. The Kurbatov-type plots were tested to determine the adsorption mechanism. The kinetics of Co2+ adsorption on NiO was best described by film diffusion model. A well-known thermodynamic equation was used to assess the enthalpy and entropy of the system. The thermodynamic data were indicative of the spontaneous nature of the endothermic sorption process of Co2+ onto the NiO.

Cation exchange removal of Cd from aqueous solution by NiO

Detailed adsorption experiments of Cd from aqueous solution on NiO were conducted under batch process with different concentrations of Cd, time and temperature of the suspension. The solution pH is found to play a decisive role in the metal ions precipitation, surface dissolution and adsorption of metal ions onto the NiO. Preliminary adsorption experiments show that the selectivity of NiO towards different divalent metal ions follows the trend Pb>Zn>Co>Cd, which is related to their first hydrolysis equilibrium constant. The exchange between the proton from the NiO surface and the metal from solution is responsible for the adsorption. The cation/exchange mechanism essentially remains the same for Pb, Zn, Co and Cd ions. The sorption of Cd on NiO particles is described by the modified Langmuir adsorption isotherms. The isosteric heat of adsorption (ΔH) indicates the endothermic nature of the cation exchange process. Spectroscopic analyses provide evidence that Cd is chemisorbed onto the surface of NiO.

Selectivity reversal and dimerization of chromate in the exchanger Amberlite IRA-400

Abstract Chromate sorption on the strong basic anion exchanger, Amberlite IRA-400 is studied as function of pH (2–11), temperature (20–40°C) and different initial concentrations (1.030–15.449 mmol/l). The sorption increases with the decrease in pH and increase in temperature. The ratios of chloride released/chromate sorbed are determined, which are found to decrease with the decrease in pH of the solution, while the effect of temperature on mole ratios is negligible. It is suggested that the chromate sorption takes place initially as CrO 4 2− followed by HCrO 4 − . The differential isosteric heats of adsorption, Δ H , are also computed which show the process to be endothermic in nature. IR spectra of chromate sorption on the chloride form of the resins have been studied as a function of pH at 20°C. These spectra reveal the dimerization of HCrO 4 − to Cr 2 O 7 2− at lower pH inside the exchanger.

Effect of Ni2+ ion doping on the physical characteristics and chromate adsorption behavior of goethite.

Pure and 0.25% Ni(2+) ion doped goethite samples, prepared by the coprecipitation method, were characterized for pH of Point of Zero Charge (pH(pzc)), Surface area, XRD, TG-DTA, FTIR and TEM. Effect of Ni(2+) ions doping on the adsorption of chromate on goethite was investigated at pH-3, -5 and -7 in the temperature range 303-323K. It was found that adsorption of chromate increases with decreasing pH and increasing temperature on both pure and Ni(2+)-doped goethite. Adsorption of chromate was found to increase from 61.4% to 82.92% with Ni(2+) ion doping in goethite matrix at the lowest pH (pH-3) and highest temperature (323K), using 1.02 mmol L(-1) chromate solution. Langmuir isotherm was found applicable to the experimental data. The values of Delta H (isosteric heat of adsorption) calculated for both the samples of goethite were positive, showing endothermic nature of the adsorption process.

Heavy metal desorption kinetic as affected by of anions complexation onto manganese dioxide surfaces.

Oxides of Fe, Al, and Mn have been studied extensively for heavy metals fixation in soil. However, little is known about the effect of anions on the desorption processes of these metals, especially from manganese dioxide. The purpose of this study was to examine the influence of residence time, temperature, and interacting anions on desorption of Pb(2+), Cd(2+) and Cu(2+) from MnO(2). MnO(2) was characterized by different experimental techniques prior to desorption studies. The sorption-desorption studies were conducted for Pb(2+), Cu(2+), and Cd(2+) ions in the presence of different electrolytes and at different temperature in the range 293-323 K. For all the sorption experiments, Pb(2+) sorption was the greatest and almost 100% sorption occurred in the presence of 0.001 M potassium phosphate. The sorption of metals under investigation followed the order Pb(2+)>Cu(2+)>Cd(2+), whereas the desorption order was Cd(2+)>Cu(2+)>Pb(2+) in 0.01 M potassium nitrate and sulphate. Only a small quantity of desorbed Pb was detected, even at the low value of pH 3. These results indicated the stability of lead phosphate precipitates or that phosphate treatment imparted stability to the ternary complexes formed at the MnO(2) surface. The detailed desorption kinetics were conducted only for Cd(2+) in 0.01 M potassium nitrate or 0.001 M phosphate at pH values of 3 and 4 in the temperature range 303-323 K. A substantial decrease in Cd(2+) desorption was noted with increasing pH and temperature and the desorption process reached equilibration in 3h at pH 4. However, at pH 3 the desorption fluctuated, which is probably due the dissolution of the solid at such low pH values.

Selective Removal of Chromates by Macroporous Exchanger Amberlyst A-21

Sorption studies of chromate on weakly basic macroporous anion exchanger Amberlyst A-21 were performed as a function of pH (2 - 9), temperature (20 - 40 °C) and concentration (0.4 - 80 mmol.l−1). Chromate sorption was observed to decrease with the increase in initial pH of the solution, with a sorption maxima at pH 2 and increased with the increase in temperature. The changes in pH and in the ratio of chloride ions released to chromate ions sorbed suggested that the anion exchange process was accompanied by hydrolysis and Donnan invasion. The FTIR spectra and isosteric heat of sorption besides showing the hydrolysis / Donnan invasion of resin under different experimental conditions of concentration, pH and temperature also showed the dimerization of the chromate species inside the resin phase.